1. Field of the Invention
The present invention relates to quick-action locking device for an electric power tool and, in particular, a circular saw and the like, and designed for securing a working tool to a motor-driven hollow spindle located in a housing of the power tool, with the quick-action locking device including a locking spindle axially displaceable in the hollow spindle of the electrical power tool, a resilient member for axially restraining the locking spindle, a locking flange cooperating with the locking spindle for securing the working tool to the hollow spindle for joint rotation therewith, and a locking lever provided at an end of the locking spindle remote from the working tool and pivotable about a pivot axis between a locking position, in which the working tool is secured to the spindle, and an exchange position in which the working tool can be replaced. The present invention also relates to an electric power tool with a quick-action locking device as described above.
2. Description of the Prior Art
Quick-action locking devices are used with the electrical power tools to provide for manual replacement of a working tool. Contrary to conventional locking devices, quick-action locking devices do not need an auxiliary tool for their locking and release. E.g., a conventional device can include a threaded rod with a locking flange, which is fixedly secured thereon, and a nut. With this device, the user has to use an auxiliary tool in form of an open-end wrench in order, e.g., to replace the working tool. Contrary to this, a quick-action locking device can be actuated with a locking lever in order to be able to replace a working tool.
A quick-action locking device is disclosed, e.g., in German Patent No. 4,336,620. The quick-action locking device disclosed in the German patent has a locking spindle axially displaceable in the hollow spindle of the electrical power tool and a resilient member for axially restraining the locking spindle. The locking device further includes a locking flange which cooperates with the locking spindle for securing the working tool to the spindle for joint rotation therewith. A locking lever is provided at an end of the locking spindle remote from the working tool for displacing the locking spindle between a locking position, in which the working tool is secured to the spindle, and an exchange position in which the working tool can be replaced. In the locking position, the working tool is located between the locking flange and the hollow spindle. At the end of the locking lever, which is secured on the pivot axis, there is provided an eccentric that is connected with the locking spindle by a bolt. Upon pivoting of the locking lever into the exchange position, the locking spindle is displaced by the eccentric axially in a direction of the working tool against the force of the resilient member and the frictional force generated between the eccentric and the bolt. In this position of the locking lever, the locking flange can be screwed out of the locking spindle without the use of any auxiliary tool, e.g., in order to replace the working tool.
The advantage of the disclosed quick-action locking device consists in that a working tool can be replaced without the user using any auxiliary tool. The user simply pivots the locking lever into its exchange position and screws the locking flange out of the hollow spindle so that he can remove the working tool or reposition it.
The drawback of the disclosed quick-action locking device consists in that the positional characteristics of the locking lever cannot be reliably maintained. If the force applied by the user is too large for the positioning process, the friction losses between the locking lever and the locking spindle are high. On the other hand, the locking lever can find itself in an intermediate position in which the locking device is neither locked nor released.
Accordingly, an object of the present invention is to provide a quick-action device for an electrical power tool which does not require application of a large force for its locking and release.
Another object of the present invention is to provide a quick-action locking device that is reliably retained in its locking and release positions.
A further object of the present invention is to provide a quick-action locking device that can be economically produced.